Catalyst for the simultaneous hydrodemetallization and hydroconversion of heavy hydrocarbon feedstocks

ABSTRACT

An improved catalyst for use in the hydrodemetallization and hydroconversion of heavy hydrocarbon feedstocks and method of making same and, more particularly, an improved catalyst having two distinct phases supported on a refractory support wherein the first phase effectively stores metals removed from the feedstock and the second phase exhibits superior catalytic acitivity for hydrogenation when processing heavy hydrocarbon feedstocks.

This is a division of application Ser. No. 042,812 filed Apr. 27, 1987,now U.S. Pat. No. 4,729,980.

BACKGROUND OF THE INVENTION

The present invention is drawn to an improved catalyst for use in thehydrodemetallization and hydroconversion of heavy hydrocarbon feedstocksand method of making same and, more particularly, an improved catalysthaving two distinct phases supported on a refractory support wherein thefirst phase effectively stores metals removed from the feedstock and thesecond phase exhibits superior catalytic activity for hydrogenation whenprocessing heavy hydrocarbon feedstocks.

Heretofore, operations such as hydrotreatment of heavy hydrocarbons areperformed in the presence of catalysts comprising elements of Group VIIIand Group VIB supported on a refractory oxide support. These types ofcatalysts suffer from a number of disadvantages. For example, during thehydrotreatment of heavy feedstocks the life of most of the conventionalcatalyst is shortened by a fast deactivation. The first cause for thedeactivation is the deposition of coke on the catalyst. Coke depositscan be avoided by improving the hydrogenation activity of the catalyst.The second cause for the deactivation results from metal deposits on thecatalyst.

Most of the patents related to improved demetallization catalysts dealwith special designs of the catalyst pore size distribution. It has beenfound in the prior art that a catalyst having a macropore structure cangenerally accumulate higher amounts of metals. In order to achieve thismacropore structure several approaches have been considered in the priorart. One of these is to vary the form and size of the catalyst particlesand the surface area and the porosity of the catalyst support. Thefollowing patents are examples: U.S. Pat. No. 4,014,821, U.S. Pat. No.4,082,695, U.S. Pat. No. 4,102,822, U.S. Pat. No. 4,297,242, U.S. Pat.No. 4,328,127, U.S. Pat. No. 4,351,717, U.S. Pat. No. 4,411,771, U.S.Pat. No. 4,414,141. The optimum pore structure appears to be well knownin the previous art. Having established the optimum pore structure, thenext step would be to optimize the chemical formulation and compositionof the catalyst.

Patents which deal with variations in the chemical composition andformulation are as follows: U.S. Pat. No. 3,898,155, U.S. Pat. No.3,931,052, U.S. Pat. No. 3,985,684, U.S. Pat. No. 4,344,867 and G.B.Pat. No. 2,032,795. The first three patents consider the inclusion of athird element besides the Group VIB and Group VIII elements in thecatalyst. U.S. Pat. No. 4,344,867 is concerned with a chemical treatmentof a catalyst support. The G.B. Pat. No. 2,032,795 patent eliminates theGroup VIB element from the composition and introduces a method of coreimpregnation for the preparation of the catalyst. All of these patentshowever are based on the fact that larger pores can accumulate higheramounts of metals. Thus, while some improvement in demetallization maybe accomplished employing these catalyst, the increase indemetallization is generally accompanied by a loss in hydrogenationactivity.

Accordingly, it is the principal object of the present invention toprovide a catalyst and method for making same which exhibits goodsimultaneous demetallization and hydrogenation activity when processingheavy hydrocarbon feeds.

It is a particular object of the present invention to provide a catalystand method for making same as set forth above having two distinct metalphases deposited on a refractory support.

It is a further object of the present invention to provide a catalystand method for making same as set forth above wherein the first phase isa demetallization phase and the second phase is a hydrogenation phase.

It is a still further object of the present invention to provide acatalyst and method for making same as set forth wherein the weightratio of the phases as measured by mossbauer spectrum are controlled.

Further objects and advantages of the present invention will appearhereinbelow.

SUMMARY OF THE INVENTION

In accordance with the present invention the foregoing objects andadvantages are readily obtained.

The present invention is drawn to an improved catalyst for use in thehydrodemetallization and hydroconversion of heavy hydrocarbon feedstocksand method of making same and, more particularly, an improved catalysthaving two distinct phases supported on a refractory support wherein thefirst phase effectively stores metals removed from the feedstock and thesecond phase exhibits superior catalytic activity for hydrogenation whenprocessing heavy hydrocarbon feedstocks. The catalyst of the presentinvention comprises a refractory support having a first demetallizationphase and a second hydrogenation phase supported thereon, the firstdemetallization phase being selected from the group consisting of ironoxide, iron sulphide and mixtures thereof and the second phase beingselected from the group consisting of iron-Group VIB metal oxides,iron-Group VIB sulphides and mixtures thereof wherein the weight ratioof the first phase to the second phase as measured by mossbauer spectrumis from about 0.1 to 8.0, the iron is present in an amount of from about4 to 20 wt.% and the Group VIB metal is present in an amount of fromabout 0.1 to 8 wt.% wherein the atomic ratio of iron to Group VIB metalis from about 0.3 to 20. In accordance with a preferred embodiment ofthe present invention, the refractory support is selected from the groupconsisting of alumina, silica, titania and mixtures thereof and has thefollowing pore size distribution:

≦90 Å diameter: between 0-10% pore volume

90-300 Å diameter: between 20-85% pore volume

300-500 Å diameter: between 5-20% pore volume

≧500 Å diameter: between 0-10% pore volume.

The method for preparing the catalyst comprises providing a refractorysupport structure, first impregnating the refractory support structurewith an acid iron nitrate solution so as to obtain a composition of fromabout 4 to 20 wt.% iron on the final catalyst, filtering, drying andcalcining the impregnated support, second impregnating the filtered,dried and calcined iron impregnated support with a solution containing aGroup VIB metallic component so as to obtain a composition of from about0.1 to 8 wt.% Group VIB metallic component on the final catalyst, andfiltering, drying and calcining the impregnated support. The process fortreating heavy hydrocarbon feedstocks with the catalyst of the presentinvention comprises contacting the feedstock with the catalyst of thepresent invention at a temperature of from about 150° to 500° C., at apressure of from about 30 to 250 atmospheres and LHSV of from about 0.1to 25 h⁻¹ in a reactor.

The catalyst of the present invention is capable of storing metalsremoved from the heavy hydrocarbon feedstock in the demetallizationphase supported on the refractory support. The iron oxide and/or ironsulphide phase can store large amounts of metals without metalaccumulating into the pores thereby avoiding structural change andcorrespondingly a decrease in activity. The catalyst offers superiorsimultaneous demetallization and hydrogenation over catalysts heretoforeknown.

DETAILED DESCRIPTION

Effective simultaneous demetallization and hydrogenation of a heavyhydrocarbon feedstock can be accomplished when employing the catalyst ofthe present invention. The term "demetallization" as used herein refersto the elimination of at least 70% of the metals in the heavy feedstockas effected by passing the feedstock through a reaction zone containingthe catalyst of the present invention.

The catalyst of the present invention comprises a refractory supporthaving a first demetallization phase and a second hydrogenation phasesupported thereon, the first demetallization phase being selected fromthe group consisting of iron oxide, iron sulphide and mixtures thereofand the second phase being selected from the group consisting ofiron-Group VIB metal oxides, iron-Group VIB sulphides and mixturesthereof wherein the weight ratio of the first phase to the second phaseas measured by mossbauer spectrum is from about 0.1 to 8.0, the iron ispresent in an amount of from about 4 to 20 wt.% and the Group VIB metalis present in an amount of from about 0.1 to 8 wt.% wherein the atomicratio of iron to Group VIB metal is from about 0.3 to 20. In accordancewith a preferred embodiment of the present invention the iron and GroupVIB metal are present in an amount of from about 4 to 20 wt.% and 1.0 to5.0 wt.%, respectively, wherein the atomic ratio of iron to Group VIBmetal is from about 0.6 to 5.0. The first phase in the preferredembodiment contains from about 30 to 85 wt.%, and preferably 30 to 70wt.% of the total iron content of the final catalyst and, when in theform of an iron sulphide, should have a crystalline structure selectedfrom the group consisting to the cubic system, the hexagonal system, themonoclinic system and mixtures thereof. The crystalline structure of thefirst phase is important only when the phase is iron sulphide. If thephase is iron oxide, crystalline structure is immaterial. This isbecause iron oxide is a precursor which would yield iron sulfide underreaction conditions. The second phase preferably contains a crystallinestructure of the cubic system and the atomic ratio of iron to Group VIBmetal is from about 0.8 to 3.0. The preferred refractory support isselected from the group consisting of alumina, silica, titania andmixtures thereof and has the following pore size distribution:

≦90 Å diameter: between 0-10% pore volume

90-300 Å diameter: between 20-85% pore volume

300-500 Å diameter: between 5-20% pore volume

≧500 Å diameter: between 0-10% pore volume.

In order to obtain the two phases on the refractory support in the finalcatalyst it is critical that the support first be impregnated with ironand thereafter impregnated with the Group VIB metal. The method of thepresent invention comprises providing a refractory support structure,first impregnating the refractory support structure with an acid ironnitrate solution so as to obtain a composition of from about 4 to 20wt.% iron on the final catalyst, filtering, drying and calcining theimpregnated support, second impregnating the filtered, dried andcalcined iron impregnated support with a solution containing a Group VIBmetallic component so as to obtain a composition of from about 0.5 to 8wt.% Group VIB metallic component on the final catalyst, and filtering,drying and calcining the impregnated support. The foregoing processresults in two phases being deposited on the refractory surface, thefirst phase being iron oxide and the second phase being iron-Group VIBoxides. If desired, the resultant catalyst can be presulphided so as toform iron sulphide and iron-Group VIB sulphide by presulphiding is at atemperature of about 250° to 450° C., a pressure of about 1 and 150atmospheres in an H₂ /H₂ S atmosphere containing between 5 to 15 wt.% H₂S.

The first demetallization phase has been characterized by its x-raydiffraction pattern and its mossbauer spectrum. The x-ray diffractionpattern of the first phase is used for the determination of the crystalstructure of the precursor iron oxide or the iron sulphide which ispresent in the presulphided catalysts. It has been found that onlycrystals of iron sulfides of the hexagonal, cubic or monoclinic systemcan store the metals removed from the oil without loss in stabilitybecause they present cation vacancies which can lodge the metal cationsfrom the crude oil.

The mossbauer spectrum allows to quantify the proportion or ratiobetween the phases. The area of the mossbauer spectrum of any compoundis proportional to its concentration. Thus, the integration of each ofthe spectrum of different compounds present in a sample would yieldtheir weight percentage. The first phase is characterized by a six linespectrum while the second phase is characterized by a doublet spectrum.The mossbauer parameters of these two phases fall in the rangesspecified as follows:

    ______________________________________                                                  Magnetic   Isomer    Quadripole                                               Field      Shift     Splitting                                      Phase     H (gauss)  IS (mms.sup.-1)                                                                         QS (mms.sup.-1)                                ______________________________________                                        First                                                                         (Oxide)   350-600    0.0-0.5   0.0-0.5                                        (Sulphide)                                                                              150-350    0.0-0.6   0.0-0.6                                        Second                                                                        (Oxide)   0          0.0-2.0   0.0-3.0                                        (Sulphide)                                                                              0          0.0-2.0   0.0-3.0                                        ______________________________________                                    

Examination of spent catalysts by mossbauer spectroscopy reveals thatthe catalyst acts to store the metal contaminants from the oil. Therelative proportion between the two phases serve to control theactivity, stability (life) and the selectivity of the catalyst.

The pore size distribution of the catalyst is important only in thesense of permitting a good diffusion of the reactant moleculesthroughout the catalyst and is preferably as follows:

≦90 Å diameter: between 0-10% pore volume

90-300 Å diameter: between 20-85% pore volume

300-500 Å diameter: between 5-20% pore volume

≧500 Å diameter: between 0-10% pore volume.

A catalyst of the present invention is useful in hydrotreatmentoperations involving heavy feedstocks. It possesses a good catalyticactivity for hydrodemetallization and hydroconversion reactions. Theheavy feedstocks to be handled in these operations might be vacuumresidues, deasphalted crudes and also heavy vacuum gas oils.

In cases where a presulphided catalyst is desirable, it should bepresulphided with a light sulphur containing feed at temperatures in therange of 250° to 450° C. at pressures between 1 and 150 atmospheres ofH₂. The H₂ /H₂ S ratio is critical in order to keep the firstphase/second phase ratio within the recommended limits. A mixturecontaining between 5 to 15% of H₂ S is adequate. The H₂ S is providedfor the sulphur compound in the presulphiding feed. Suitable sulphurcompounds are H₂ S, CS₂, mercapthans, and/or any organic sulphurcompound.

The shape and/or the size of the catalyst is not limiting. It can beused in any shape or size, in a fixed bed reactor, stirred tank and/orslurry. The process operation consists of contacting the feed with thecatalyst in the presence of hydrogen under the following conditions:temperature of between 150° to 500° C., preferably 250° to 480° C.,pressure of between 30 to 250 atms., preferably 50 to 150 atms., andLHSV (h⁻¹) of between 0.1 to 25, preferably 0.1 to 15.

The following examples are given in order to more fully describe, butnot to limit, the invention.

EXAMPLE 1

A catalyst was prepared by consecutive impregnation of pellets of γ-Al₂O₃ support. Iron was firstly impregnated using an acid iron nitratesolution containing 1.12 mol. per liter solution of iron. A solutionvolume of twice the pore volume of the support was employed. Thecatalyst was then carefully washed, filtered dried and calcined.Molybdenum was impregnated secondly, using an ammonium heptamolybdatesolution containing 0.20 mol. per liter solution of molybdenum. Aprocedure similar to that employed with iron was then followed. Thefinal catalyst had the following physical and chemical properties:

Physical Properties

Surface Area: 145 m² g⁻¹

Pore Volume: 0.81 cc g⁻¹

Pore Size Distribution: % pore volume

Diameter (Å):

<90: 8.5

90-300: 62.2

300-500: 23.7

>500: 5.6

Chemical Properties

Fe: 6 %w

Mo: 2 %w

The catalyst was grounded to a 15 μm average presulphided at 350° C.,1.2 atmosphere of pressure using a mixture of H₂ /H₂ S at a ratio of1:10. The sulphided catalyst was analyzed by x-ray diffraction andmossbauer spectroscopy. The results indicated that two iron compoundswere present, namely:

Hexagonal Fe₇ S₈ : 40% of total iron

Cubic Fe_(x) Mo_(y) S_(z) : 60% of total iron

The mossbauer parameters of these two compounds were measured asfollows:

    ______________________________________                                                Magnetic Isomer    Quadripole                                                 Field    Shift     Splitting                                                  H (gauss)                                                                              IS (mms.sup.-1)                                                                         QS (mms.sup.-1)                                    ______________________________________                                        Fe.sub.7 S.sub.8                                                                        226-302    0.6        0.0-0.25                                      (6 lines)                                                                     Fe.sub.x Mo.sub.y S.sub.z                                                               0          0.3-1.5   0.8-2.5                                        (2 lines)                                                                     ______________________________________                                    

The catalytic activity was evaluated in a 3.5 liter autoclave under thefollowing conditions:

Temperature: 450° C.

H₂ pressure: 1900 psi

H₂ flow rate: 16 l min⁻¹

Duration: 5 h

Catalyst: 8 %w

Feed: 1000 g

The feed was a heavy vacuum residue Zuata feedstock having the followingproperties:

API gravity: 2.2°

Sulphur content: 4.9%

Vanadium content: 750 ppm

Asphaltenes: 25 %w

Conradson Carbon: 27 %w

The results of the catalytic activity test are as follows:

HDM: 98

HDS: 70

Asphaltene Conversion: 95

Conradson Carbon Conversion: 94

API Gravity Variation: 25.2

As can be seen from the foregoing, the catalyst of the present inventionis extremely effective in the demetallization and hydrogenation of heavyfeedstocks.

EXAMPLE 2

The initial activity of the catalyst of Example 1 in pellet form, and aconventional commercial catalyst of CoMo-type having a similar pore sizedistribution and a Co content of 2.5 %w and Mo content of 12.3 %w wereevaluated in a Carberry reactor using the following conditions:

Temperature: 400° C.

H₂ pressure: 1500 psi

Catalyst: 6%

Feed: 600 g

The feedstock was a deasphalted Morichal having the followingproperties:

API gravity: 16.7°

Vanadium content: 150 ppm

Sulphur content: 2.4% w

Asphaltenes: 2.4% w

Conradson Carbon: 5.1

The two catalysts were subjected to three consecutive runs, (withintermediate xylene washing) and evaluated under the same conditions, inorder to determine the final activity of a partially deactivatedcatalyst. The results are summarized in Table I.

                  TABLE I                                                         ______________________________________                                        CATALYTIC ACTIVITY OF NOVEL                                                   CATALYST AND CONVENTIONAL CATALYST                                                         FeMoAl     CoMoAl                                                Activity       Initial  Final   Initial                                                                              Final                                  ______________________________________                                        HDM            70       65      90     10                                     HDS            35       15      98     35                                     HDC.sub.540 +  75       100     65     34                                     Asphaltene Conversion                                                                        78       78      92     66                                     Conradson Carbon                                                                             50       61      55     47                                     Conversion                                                                    ______________________________________                                    

As can be seen from Table I the life of the catalyst of the presentinvention is superior to known catalysts.

EXAMPLE 3

A test was carried out similar to Example 2 above but using threeadditional feedstocks which consist of the same DAO diluted in light gasoil at different proportions, so as to give the following vanadiumcontents (ppm):

Feed 1: 150

Feed 2: 100

Feed 3: 30

The vanadium removal (HDM) and the conversion of the 540° C.⁺ fraction(HDC₅₄₀ +) were evaluated, the results were as follows:

    ______________________________________                                               Feedstocks                                                                    1         2           3                                                       FeMo  CoMo    FeMo    CoMo  FeMo  CoMo                                 ______________________________________                                        HDM Initial                                                                            75      92      78    94    80    95                                 Final    73      15      76    45    78    86                                 HDC Initial                                                                            85      70      88    75    92    80                                 Final    98      55      100   68    100   72                                 ______________________________________                                    

Again the superiority of the catalyst of the present invention isdemonstrated, when metal concentration in the feed is high.

EXAMPLE 4

A series of catalysts were prepared as in Example 1 to yield differentfirst phase/second phase and Fe/Mo ratios. The catalysts were notpresulphided. The chemical composition of these catalysts is shown inTable II.

                  TABLE II                                                        ______________________________________                                                        First Phase/                                                  Catalyst                                                                             Fe/Mo    Second Phase                                                                             First Phase                                                                            Second Phase                              ______________________________________                                        1      35       10         α-Fe.sub.2 O.sub.3                                                               α-FeMoO.sub.4                       2      8.0      4.5        α-Fe.sub.2 O.sub.3                                                               α-FeMoO.sub.4                       3      3.9      2.5        γ-Fe.sub.2 O.sub.3                                                               α-FeMoO.sub.4                       4      2.8      1.4        γ-Fe.sub.2 O.sub.3                                                               α-FeMoO.sub.4                       5      2.0      0.5        γ-Fe.sub.2 O.sub.3                                                               α-FeMoO.sub.4                       6      0.9      0.0        --       α-FeMoO.sub.4                       7      0.7      0.05       α-Fe.sub.2 O.sub.3                                                               α-FeMoO.sub.4                       8      0.4      0.08       α-Fe.sub.2 O.sub.3                                                               α-FeMoO.sub.4                       9      0.3      0.15       α-Fe.sub.2 O.sub.3                                                               β-FeMoO.sub.4                        10     0        No Iron                                                       ______________________________________                                    

The catalytic activity and stability was evaluated in the same manner asin Example 2, however, the catalysts were used in the oxide form (asidentified in Table II). The results are reported in Table III.

                  TABLE III                                                       ______________________________________                                                                             Conradson                                                    HDC      Asphaltene                                                                            Carbon                                   HDM        HDS      540.sup.+                                                                              Conversion                                                                            Conversion                               Catalyst                                                                             I     F     I   F    I   F    I    F    I    F                         ______________________________________                                        1      10     8     2   2   15  13   10    8    7    8                        2      54    52    18  17   56  54   68   55   25   24                        3      62    58    19  20   65  67   73   62   32   29                        4      68    64    20  19   70  72   75   73   48   46                        5      71    65    24  15   75  100  78   78   50   60                        6      92    38    43  12   88  25   95   42   82   28                        7      90    55    40  16   84  52   92   50   75   36                        8      86    70    39  20   83  61   88   78   70   42                        9      84    73    39  20   80  68   86   65   68   49                        10     86    25    33  12   80  20   88   18   70   20                        ______________________________________                                         I -- Initial                                                                  F = Final                                                                

Table III demonstrates the criticality of iron-Group VIB metal ratio andthe first phase/second phase ratio on hydrodemetallization andhydroconversion.

EXAMPLE 5

Catalyst No. 5 of Example 4 was presulphided at different H₂ S/H₂ratios. The iron sulphide of the first phase exhibited the followingcrystal structures.

    ______________________________________                                        No.    H.sub.2 S/H.sub.2                                                                         Crystal System                                                                              First Phase                                  ______________________________________                                        5-1    1:5         Cubic         Fe.sub.1-x S                                 5-2    1:10        Monoclinic    Fe.sub.y S.sub.8                             5-3    1:15        Hexagonal     Fe.sub.y S.sub.8                             5-4    1:20        Hexagonal     FeS                                          5-5    1:30        Tetragonal    FeS                                          ______________________________________                                    

The initial catalytic activity was measured in the same manner as inExample 2. The results were as follows:

    ______________________________________                                        HDM                HDS    HDC.sub.540+                                        ______________________________________                                        5-1     72             43     48                                              5-2     75             28     62                                              5-3     85             22     39                                              5-4     50             10     20                                              5-5     35              8     15                                              ______________________________________                                    

The foregoing demonstrates the criticality of the crystal structure ofthe first phase on activity.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:
 1. A process for the hydrodemetallization,hydrodesulfurizing and hydrocracking of heavy hydrocarbon feedstockswhich comprises contacting the feedstock with a catalyst comprising arefractory support having a first demetallization phase and a secondhydrogenation phase supported thereon, said first demetallization phasebeing selected from the group consisting of iron oxide, iron sulphideand mixtures thereof and said second hydrogenation phase being selectedfrom the group consisting of iron-Group VIB metal oxides, iron-Group VIBmetal sulphides and mixtures thereof wherein said weight ratio of saidfirst phase to said second phase is measured by mossbauer spectrum isfrom about 0.1 to 8.0; said iron is present in an amount of from about 4to 20 wt.% and said Group VIB metal is present in an amount of fromabout 0.1 to 8 wt.% wherein the atomic ratio of iron to Group VIB metalis from about 0.3 to 20, at a temperature of from about 150° to 500° C.,at a pressure of from about 30 to 250 atmospheres and LHSV, LiquidHourly Space Velocity, of from about 0.1 to 25 h⁻¹ in a reactor.
 2. Aprocess according to claim 1 including contacting the feedstock at atemperature of about 250° to 480° C. at a pressure of about 50 to 150atmospheres and LHSV of about 0.1 to 15 h⁻¹.
 3. A process according toclaim 1 wherein the feedstock is a heavy vacuum residue.
 4. A processaccording to claim 1 wherein the feedstock is a deasphalted crude.
 5. Aprocess according to claim 1 wherein the feedstock is a heavy vacuum gasoil.
 6. A process according to claim 1 wherein the refractory support isselected from the group consisting of alumina, silica, titania andmixtures thereof and has the following pore size distribution:≦90 Ådiameter: between 0-10% pore volume 90-300 Å diameter: between 20-85%pore volume 300-500 Å diameter: between 5-20% pore volume ≧500 Ådiameter: between 0-10% pore volume.